how much power to a rack in a datacenter?

Unanswered Question
Aug 6th, 2009

stupid question but how do you determine how much power to run to a rack in a datacenter?

say we have a new rack going in where 24 of the 44 u's will be filled with ASAs and 2960s drawing 2.5-3a (based on documentation). Does that mean 24x3? I need at least 72 amps run to the rack? So thats 3 30 amp circuits (which each have a PDU rated at 24a)?

We all know that every device isnt going to be drawing the full 3a at all times (or probably even at any given time)...so is there some best practices documented somewhere that dictate you multiple total amperage by a factor of .3 or something and build out the rack to that spec? Or should we be doing just what I described above, adding up the peak draw of every device in the rack?

I have this problem too.
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cadillaccanopy Wed, 09/02/2009 - 19:30

Hi slug420,

Power supply max's wont get you anywhere. you'll be seriously overpowered. What you need, is for somebody to get an ammeter, and measure it. Add an "oops" margin, whatever makes you comfortable, and one you can sell to your inspector that it meets NEC guidelines.

Add your margin per the total on each circuit/PDU.

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